How to show If else condition in a UML system sequ

Question

Is it possible to describe an if-else structure in a system sequence diagram? If yes, how is this done?

Answer 1

Yes. This can be done in sequence diagrams. Not only if else,You can show loops, breaks and parallel etc.You have to learn combined fragment which is a sub-type of interaction fragment, to do that.

Answer 2

Here's more info about combined fragments from the VS 2010 sequence diagram documentation:

• UML Sequence Diagrams: Reference
• UML Sequence Diagrams: Guidelines
• Describing Control Flow with Fragments in UML Sequence Diagrams

Answer 3

Yes, this can be done in UML 2 using the 'Alternative' combined fragment type, although personally I find them relatively difficult to read. There is a good example in this IBM DeveloperWorks article.